The present disclosure relates to a motor controller for motor-driven compressor. The motor-driven compressor has a motor and a compressing body. The motor-driven compressor compresses and discharges refrigerant.
To cool the motor, this type of motor-driven compressor has the coil of the motor in an area where drawn refrigerant exists (see, for example, Japanese Laid-Open Patent Publication No. 2009-250123). If the motor is in a stopped state for a long time, the refrigerant liquefies in the area where the coil is mounted, and the coil is exposed to accumulated liquid refrigerant. Accordingly, when the motor is started, the coil may experience an electric leak as a result of the exposure of the coil to liquid refrigerant. Particularly, when the voltage supplied to the coil varies to a great extent, such an electric leak is more likely to occur.
An inverter is employed to control operation of the motor. The disclosure described in the aforementioned document uses a transformer circuit for transforming the voltage supplied to the inverter. The transformer circuit is controlled by a voltage control section. The voltage control section controls the transformer circuit to supply a low voltage to the inverter when liquid refrigerant is accumulated in the housing. When it is determined that liquid refrigerant has not accumulated in the housing, the voltage control section switches from a low voltage to a high voltage. The disclosure of the aforementioned document aims to, through such voltage control, prevent an electric leak by lowering the voltage when liquid refrigerant is accumulated in the area in which the coil is arranged.
Controls performed on inverters include a three phase modulation control and a two phase modulation control. The two phase modulation control has the advantage that loss of the inverter (switching loss of the inverter) is relatively low compared to the three phase modulation control.
However, the two phase modulation control is achieved by varying the voltage of the motor at the neutral point in the three phase modulation control. Accordingly, if liquid refrigerant is accumulated in the housing and thus the stray capacitance between the housing and the coil is lowered, an electric leak is more likely to occur in the two phase modulation control than in the three phase modulation control.
Accordingly, it is an objective of the present to reduce loss of the inverter in a motor-driven compressor and decrease the likelihood of an electric leak.